The present disclosure relates to a semiconductor component with vertical structures having a high aspect ratio, and to a method for producing it.
Such component may be a MOS transistor and may include a drift control zone that is arranged adjacent to a drift zone and that is dielectrically insulated from the drift zone by a dielectric layer. In the case of the component, the drift control zone serves for controlling a conducting channel in the drift zone if the component is driven in the on state.
One problem in the operation of MOS transistors arises when avalanche breakdown occurs. The electric field strength in the component increases as the reverse voltage increases to such an extent until at a critical field strength—the breakdown field strength—free charge carriers within the free path length between two impacts with the crystal lattice take up so much energy from the electric field that, upon the next impact, they ionize the semiconductor atom hit and generate an electron-hole pair and hence further free charge carriers, which are accelerated again by the electric field. This avalanche-like multiplication of charge carriers commences particularly at inhomogeneities in the component, because spikes of the electric field strength are present there, and upwardly limits the maximum reverse voltage maintained by the component. This maximum maintained reverse voltage when avalanche multiplication is used is referred to hereinafter as blocking capability or dielectric strength of the semiconductor component. In a corresponding manner, partial regions of the semiconductor component can also have such a blocking capability.
If an avalanche multiplication of this type takes place in the vicinity of a dielectric, for example the dielectric separating the drift zone and the drift control zone or a gate dielectric that dielectrically insulates a gate electrode from a body zone, then the dielectric can be damaged by the fast charge carriers generated during the avalanche multiplication.
In the case of a component having a drift zone and a drift control zone, the problem of an avalanche breakdown occurring near the dielectric is additionally intensified by the fact that interface charges are present at the interface between the drift zone and the dielectric. The charges can bring about a curvature of the eqipotential areas in that region of the drift zone which adjoins the dielectric, such that the breakdown voltage of the semiconductor material, when the reverse voltage increases, is reached there more readily than in the sections of the drift zone which are spaced apart further from the dielectric. An avalanche breakdown thereby commences directly at the dielectric.
For these and other reasons, there is a need for the present invention.